The overall goal of the proposed research is to identify and functionally characterize subpopulations of rabbit lymphocytes. Monoclonal antibodies (MAb) against rabbit lymphocyte surface antigens will be obtained from hybridomas produced by the fusion of mouse myeloma cells with spleen cells of mice immunized with rabbit by lymphoid cells. The cellular and tissue distribution of cell surface antigens identified by these MAb's will be examined by membrane immunoflurorescence, both visually and with a fluorescence activated cell sorter (FACS). The biochemical nature of the antigens recognized by these MAb's will be examined by immunoprecipitation studies with cell lysates of radioactively labeled lymphoid cells. Subpopulations of lymphocytes identified by the MAb's will be functionally characterized in a variety of immunological assays such as their responsiveness to mitogens, to antigen stimulation, and their role in secondary in vitro antibody responses and in suppression of the immune response. For these experiments, the cells tested will either be lymphoid cells, e.g., spleen depleted of a particular subpopulation, or the purified subpopulation of cells as obtained from the FACS. These studies should provide considerable insight into the cellular immune system of the rabbit.